If you could somehow use the LHC's main 7TeV beam as a rocket exhaust, and disregarded the mass of the accelerator itself, how effective would it be? (The specific situation I'm thinking of involves a portal inside the accelerator connected to the end of a spaceship, but that's not important to the question) Is a stream of light but extremely energetic matter cost-effective, or would it be better to use heavier but slower particles?

The problem, as I understand it, is that a ring-shaped particle accelerator spend a lot of its energy on using magnetic fields to bend the particles' paths into a circle, rather than on making the particles go faster. You would get much better efficiency out of a linear accelerator instead (which would thus act as a supercharged low-mass-flow ion thruster).

Robert'); DROP TABLE *; wrote:If you could somehow use the LHC's main 7TeV beam as a rocket exhaust, and disregarded the mass of the accelerator itself, how effective would it be? (The specific situation I'm thinking of involves a portal inside the accelerator connected to the end of a spaceship, but that's not important to the question) Is a stream of light but extremely energetic matter cost-effective, or would it be better to use heavier but slower particles?

Even better if you could put one end of the portal inside the Sun--instant fusion-powered rocket without needing the fusion reactor or fuel tanks. With the impulse and mass ratio you could get from that, you could thrust with all of the acceleration that your crew can withstand, more or less indefinitely, making for an ideal relativistic time-dilation starship.

ijuin wrote:Even better if you could put one end of the portal inside the Sun--instant fusion-powered rocket without needing the fusion reactor or fuel tanks. With the impulse and mass ratio you could get from that, you could thrust with all of the acceleration that your crew can withstand, more or less indefinitely, making for an ideal relativistic time-dilation starship.

I feel like the irradiation to your crew might be a little problematic. Putting the other end of the portal inside Jupiter would give you a flow of metallic liquid hydrogen at upwards of 3,500 GPa without any ill effects.

Such a system would actually conserve energy and momentum. Well, almost. The only energy not conserved is the gravitational potential energy of the stuff moving through the portal.